A motor driving device including an inverter and a current sensor is known as described in Patent Literature 1, for example. The inverter includes a U-phase arm, a V-phase arm, and a W-phase arm. These three arms are connected with a motor generator. Each of the three arms is connected in parallel between a power supply line and a ground line and has a uniform configuration.
The inventors of the present application have found the following. The U-phase arm described in Patent Literature 1 includes two non-type transistors, two spacers, a positive electrode plate, an electrode plate, an output electrode plate, a negative electrode plate, a conductor, and a current sensor. An emitter of the first non-type transistor is fixed to the positive electrode plate, while a collector of the first non-type transistor is fixed to the electrode plate via the first spacer. An emitter of the second non-type transistor is fixed to the output electrode plate, while a collector of the second non-type transistor is fixed to the negative electrode plate via the second spacer. The electrode plate and the output electrode plate are electrically connected with each other via the conductor. The current sensor is disposed in the vicinity of the conductor.
In the structure of the U-phase arm described herein, a current flows from the first non-type transistor to the output electrode plate via the conductor in an ON-state of the first non-type transistor and an OFF-state of the second non-type transistor. On the other hand, a current flows from the output electrode plate to the second non-type transistor without passing through the conductor in an OFF-state of the first non-type transistor and an ON-state of the second non-type transistor. In this case, the current flowing in the conductor does not correspond to the current input to and output from the two non-type transistors. In the structure in which the current sensor is disposed in the vicinity of the conductor, a magnetic field generated by a flow of a current in the conductor permeates the current sensor. In this condition, the current itself input to and output from the two non-type transistors (power elements) cannot be detected.